1. Field of the Invention
The present invention relates to semiconductor devices, display devices, manufacturing methods thereof, or methods for using the semiconductor devices or the display devices. In particular, the present invention relates to liquid crystal display devices including light-transmitting semiconductor layers, manufacturing methods thereof, or methods for using the liquid crystal display devices.
2. Description of the Related Art
In recent years, flat panel displays such as liquid crystal displays (LCDs) have been widely used. In particular, active matrix LCDs including a thin film transistor in each pixel have been often used. Further, a display device in which one or both of a source driver (a signal line driver circuit) and a gate driver (a scan line driver circuit) are formed over the same substrate as a pixel portion has developed. As the thin film transistor, a thin film transistor including amorphous silicon or polysilicon (polycrystalline silicon) as a semiconductor layer has been widely used.
Instead of such silicon materials, light-transmitting metal oxides have attracted attention. For example, In—Ga—Zn—O-based oxides and the like have been expected to be used as semiconductor materials needed in display devices such as liquid crystal displays. In particular, application of the In—Ga—Zn—O-based oxides and the like to channel layers of thin film transistors has been considered. Further, a technique for improving the aperture ratio with the use of a light-transmitting electrode as a gate electrode, a source electrode, or a drain electrode has been studied (see References 1 and 2).